Electrophotographic printing systems typically generate prints that are highly valued for their excellent image quality and durability. Such prints become even more valid when combined to form bound products such as books, cards, photobooks, and the like. Accordingly electrophotographic printing systems that can automatically bring prints together are highly desirable.
However, it is not a simple task to bind a stack of pages to make bound product. Conventionally this is done using staples, stitches, or adhesives as is shown for example in JP 09-109587 entitled “Document Binding Apparatus”, filed on Oct. 21, 1995, and in JP 09-110285 entitled “Bookbinding Device and Image Forming Device”, published on Apr. 28, 1997, and is practiced by the Standard Accubind Pro bookbinder and the MEM AutoBook Bookletmaker sold by Whitaker Brothers, Rockville, Md., USA. It will be appreciated that such approaches require the use of additional consumables to bind the pages and further that in many cases it is necessary to provide several different types of consumables to achieve binding that has a desirable aesthetic appearance. For example, where a single size of adhesive tape is used as binding material, the adhesive tape will have a width that is sized to extend across a stack thickness of a maximum number of prints in the stack. However, where such a single tape is used to bind only a few prints together, excess adhesive material is provided and this excess adhesive material can for example, negatively impact the appearance of the bound product. Alternatively, to the extent that an electrophotographic printing system requires the use of multiple different sizes of binding tape can be used but this in turn creates supply, loading and other logistical problems.
In the area of electrophotographic printing, it has long been proposed to use electrophotographic toner to bind two or more prints together. Typically, this involves applying toner to a page for the dedicated purpose of being used for page binding purposes. The dedicated toner is then fused for a first time to the page. The page with the toner fused to it is stacked with another page or folded onto itself. Pressure and heat are applied across page where the dedicated toner is fused to cause the dedicated toner to fuse for a second time to bind the pages. Examples of this include, U.S. Pat. No. 3,793,016, entitled “Electrophotographic Sheet Binding Process” issued Feb. 19, 1974, which describes the formation of a high density area of toner on a set of sheets and re-fusing the toner between adjacent overlaying sheets to provide bound stacks without requiring additional binding material. Further examples of this approach can be found in U.S. Pat. No. 3,794,550 entitled: “Sheet Binding”, issued Feb. 26, 1974, U.S. Pat. No. 5,014,092 entitled: “Image Forming Apparatus with a Binding Function” issued May 7, 1991, U.S. Pat. No. 4,343,673, entitled: “Binding Apparatus and Method” issued Aug. 10, 1982, U.S. Pat. No. 5,582,570, entitled: “Method and Apparatus for Binding Sheets Using a Printing Substance” issued Dec. 10, 1996, U.S. Pat. No. 6,485,606 entitled: “Apparatus for Binding Sheet Media” issued Nov. 26, 2002, Japanese Publication No. 9-110051, published on Apr. 28, 1997, and in JP Publication No. 61-274764.
In such systems, all of the heat used for binding is conveyed into the pages of stack through a top page and a bottom page of the stack. The heat applied at these points must penetrate through the entire thickness of the stack with enough intensity to fuse toner in the middle of the stack. Accordingly, where there are many pages in the stack the amount of heat that must be applied to the top page and to the bottom page to fuse all of the toner provided for binding purposes in such a manner is significant. Further, such heat must be applied over a meaningful amount of time so as to prevent overheating of the top page and bottom page of the stack while still delivering the requisite thermal energy. Both the amount of heat required and the amount of time required increase with the number of pages in the stack.
Importantly, it is to be understood that the heat that is introduced into a stack in this manner does not propagate only through the portion of the pages in the stack having toner that is applied for binding. Instead such heat propagates along the length of the pages as well. This has the effect of heating portions of the pages that are that are not used for binding. Given the amount of heat that must be applied to a stack and the amount of time required to fuse all of the dedicated toner in a stack, the propagation of heat along the pages can cause toner other than the dedicated toner to fuse causing unwanted binding and image damage to images printed on the pages.
Accordingly, other approaches have been proposed for binding stacks of prints using thermally fusable toner as an adhesive. For example, in the '550 patent and the '016 patent it is proposed that a heated dual platen system have “additional heating means provided in a bottom surface against which a stack abuts” and that chemical, pressure or other fusing techniques be used. While additional heat will increase the probability of good binding, such additional heat can increase the total amount of heat applied to the stack and can increase the risk that toner that is fused to a page for a purpose other than binding will be fused in addition to the dedicated toner used for binding.
Alternatively, U.S. Pat. No. 5,582,570, entitled “Method and Apparatus for Binding Sheets using a Printing Substance”, issued Dec. 10, 1996, describes a method and apparatus for binding sheets using a reactivatable printing substance such as toner. The apparatus comprises a printing device for applying printing toner to a binding edge of a sheet. Printing text can be applied simultaneously to the sheet by the printing device. The sheet is transferred through a preheat station to an overlay location where additional sheets having strips of toner adjacent to a binder edge thereof are overlaid, one at a time. As each sheet is overlaid, the toner strip on the preceding sheet is fused to the uppermost sheet. Such fusing can be accomplished using a heated platen or wheel that bears upon the uppermost sheet.
This one page-at-a time approach to fusing limits the amount of heat that must be passed through any individual sheet in a stack but can have the effect of reducing output speeds.
Further, it is not clear that the problem of unwanted heating of image forming toner during a second fusing is resolved by fusing one page at a time. For example, the '764 publication discloses a system that is used in cementing products of paper, sheets, etc. especially inscription sheets e.g. single sheet letters. In this system an adhesive is applied at predetermined fixed adhesive points of the product intended for copying printing, etc., then fixed and again activated and thus converted into an adhesive state. The points of the product to be adhered can be cemented together. The adhesive points are produced by means of electrostatic charge. Similarly, the above-referenced '051 publication is directed to solving the problem of easily and costlessly making envelopes without applying an expensive adhesive. In this publication, a toner image for sticking is formed on a part of the peripheral edge and the folding part of a paper. After the paper, has been folded in two, with the toner image at the inside, the part of the toner image is pressed with heat to melt the toner and bind the paper. In this way, the peripheral edge of an envelope is sealed. However, U.S. Pat. No. 7,260,354, entitled “Image Forming Method” issued on Aug. 21, 2007, notes that the heat and pressure applied to cause the toner used for binding in the '764 and '051 publications to fuse for the second time causes the toner for the image portion to fuse resulting in adhesion throughout the toner image. As a result, the toner image is said to deteriorate.
As an alternative, the '345 patent, and JP Publication 2004-126,229, propose the use of special toners that are formulated to include an adhesive that can bind pages together without heating the pages to temperatures that will cause the toner used for image forming to fuse. Specifically, the '345 patent proposes the use of a special toner that fuses at a temperature that is lower than a temperature of the toner used for image formation, while the '229 publication discloses the use of a toner having a pressure sensitive adhesive that can be deposited as a toner and made adhesive by application of pressure in a subsequent binding process. Similarly, U.S. Pat. No. 5,521,429 discloses using toners having and ultraviolet light activated adhesives.
It has also been proposed to apply energy to a stack that will cause the toner in the stack to heat from within. For example, the '429 patent also discloses applying vibration and pressure to generate heat in the fusing heat in the stacks, while U.S. Pat. No. 6,294,728, entitled “Binding Sheet Media Using Imaging Material” issued on May 28, 2002 describes a system that uses two bars to apply pressure and heat for fusing toner bearing sheets but notes that for large stacks of paper it may be necessary to heat through the stack and that additionally a variety of techniques can be used for this purpose including, ultrasound magnetic energy radio frequency energy and other forms of electromagnetic energy.
In summary, despite many decades of development, what is still needed in the art is a method that allows electrophotographic prints to be thermally bound together using a conventional toner while protecting images formed on the prints.